Recently, such electronic devices as communication, video and audio devices are used more and more in portable applications.
A lighted switch in conventional portable electronic devices has been lighted by employing either a bullet-type LED in the vicinity of a contact part of the switch or a chip-type LED in the vicinity of the switch, and providing such light guiding plate as transparent acrylic plate to guide the light to the switch section.
A lighted switch comprising opposing films or glasses with a transparent electrodes on a diffusion-type EL sheet is also known.
However, in such constitution of employing a chip-type LED in the vicinity of the switch, and guiding the light by means of a light guiding plate, it has been a problem that a loss of light and unevenness in brightness are significant, and an attempt of reducing the loss and unevenness causes increase in size and weight, leading to higher power consumption of LED and earlier exhaust of a battery in a portable device, so that the portable device cannot be used continuously for a long time.
A switch with transparent electrodes provided in opposition to each other on an EL sheet is advantageous in that very uniform illumination can be obtained, and a loss is insignificant, while it has been a problem that it lacks operational feeling as a switch.
Further, although a sputtered film of indium tin oxide (hereinafter ITO) is employed as a transparent electrode in a conventional diffusion-type EL sheet, because it is excessively stretched and bent in a process of shaping a diaphragm portion, it has been a problem that ITO may be relatively easily broken during the shaping process or operation of the diaphragm portion, and no light is emitted by the diaphragm portion due to breakage of a binder resin in a light emitting layer or dielectric layer.